Colloidal Catchment Response To Snowmelt And Precipitation Events Differs In A Forested Headwater Catchment

Climate change affects the occurrence of high-discharge (HD) events and associated nutrient exports in catchment stream water. Information on colloidal events-based losses of important nutrients, such as organic C(C-org), N, P, and S, remain relatively scarce. We hypothesized that contributions of colloidal exported N, S, and P due to differing hydrological mechanisms vary between HD events in late winter and spring. We examined one combined snowmelt and rainfall event (March 2018) with one rainfall event (May 2018) for temporal C-org, N, P, and S dynamics. The catchment exports of colloids and their subset nanoparticles were analyzed by asymmetric-flow field flow fractionation (P) and a filtration cascade (N and S). The C-org source in both events was assessed by delta C-13 composition of the stream water in relation to that of the soil. In winter, <6% of stream water P was transported by colloids (>0.1 mu m), but this was 29-64% in spring and was associated with C-org, Fe, and Al. Colloidal N and particulate S (>1 mu m) were higher during both events, but the majority of losses were dissolved (<0.1 mu m). The delta C-13 values of dissolved organic matter (C-13(DOM)) showed that in winter, most C-org was exported from the hydrologically connected hillslopes by water flowing through mineral horizons, due to snowmelt. During and after the rainfall events, export from organic horizons dominated the nutrient losses as particulates, including colloids. These events highlight the need for a better quantification of often underreported particulate, colloid, and nanoparticle contributions to weather-driven nutrient losses from catchments.